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Re: Faster compilation speed
- From: Daniel Berlin <dberlin at dberlin dot org>
- To: Cyrille Chepelov <cyrille at chepelov dot org>
- Cc: gcc at gcc dot gnu dot org
- Date: Sat, 10 Aug 2002 20:33:53 -0400 (EDT)
- Subject: Re: Faster compilation speed
- Reply-to: dberlin at dberlin dot org
On Sat, 10 Aug 2002, Cyrille Chepelov wrote:
> Le Sat, Aug 10, 2002, à 08:32:26AM -0500, Robert Lipe a écrit:
> > Linus Torvalds wrote:
> > > One fundamental fact on modern hardware is that data cache locality is
> > > good, and not being in the cache sucks. This is not likely to change.
> > This is a fact.
> > Measuring this sort of thing is possible. (Optimizing without
> > measuring is seldom a good idea.) In the absence of processor pods
> > and bus analyzers, has anyone thrown gcc at a tool like 'valgrind' or
> > cachegrind?
> I just did (I was forming the idea while reading the thread, but you beat me
> in suggesting it before I implemented it).
> I have tried on a grand total of three files, two from today's mainline CVS
> (updated from anonymous about four hours ago), and one from Linux 2.5.30; as
> my machine is not exactly the dual-multi-gigahertz, "HT"-interconnected
> (HyperTransport ?) with gobs of memory bandwith (and what else? 64 bits?)
> monsters Linus has been bragging about recently, please bear with lack of
> patience to run CG over the whole aforementioned packages...
The numbers I get on a p4 with cachegrind are *much* worse in all cases.
The miss rates are all >2%, which is a far cry from 0.1% and 0.0%.
Are you sure you have valgrind configured right for your cache?
I'm going to do this the *real* way, using the performance monitoring
counters on my p4, and get *real* numbers.